This invention relates to a system and method for reducing cold-start emissions and more particularly, to a system and method for reducing vehicle emissions which synergistically utilizes variable valve timing, ignition timing and air/fuel ratio enleanment strategies to achieve rapid catalyst xe2x80x9clight offxe2x80x9d, thereby reducing emissions during cold-start conditions.
Automotive vehicles having internal combustion engines typically utilize a three-way-catalyst (xe2x80x9cTWCxe2x80x9d) to reduce tailpipe emissions. Particularly, the TWC catalytically reduces nitrogen oxides (NOx) and oxidizes carbon monoxide (xe2x80x9cCOxe2x80x9d) and unburned hydrocarbons (xe2x80x9cHCxe2x80x9d) which are produced during the combustion process. The TWC has a very high conversion efficiency once the catalyst has xe2x80x9cwarmed upxe2x80x9d and the air/fuel ratio of the mixture is near its stoichiometric point.
The point in time at which the catalytic converter reaches a fifty percent (50%) efficiency is commonly referred to as its xe2x80x9clight-offxe2x80x9d time. Due to the relatively poor efficiency of the catalytic converter prior to xe2x80x9clight-offxe2x80x9d, recent efforts to reduce tailpipe emissions have concentrated on reducing the xe2x80x9clight-offxe2x80x9d time, thereby reducing the time during which the catalytic converter is least efficient. These prior efforts have also included concomitantly altering the air/fuel ratio and/or retarding the spark calibration of the engine. These efforts are commonly referred to as Coordinated Strategies for Starting with Reduced Emissions or xe2x80x9cCSSRExe2x80x9d, and are described for example and without limitation in U.S. Pat. Nos. 5,483,946 and 5,584,176, which are fully and completely incorporated herein by reference.
These prior efforts have suffered from some drawbacks. Particularly, the difficulty in controlling the combustion quality and stability of the engine, noise and vibration harshness, and vehicle xe2x80x9cdrivabilityxe2x80x9d as the vehicle warms up limit the application of these prior strategies.
There is therefore a need for a system and method for reducing vehicle cold-start emissions which overcomes the drawbacks of prior emissions reducing methods, strategies and systems.
It is a first object of the invention to provide a system and method for reducing vehicle cold-start emissions which overcomes at least some of the previously delineated drawbacks of prior emissions reducing methods and strategies.
It is a second object of the invention to provide a system and method for reducing vehicle cold-start emissions which synergistically utilizes variable valve timing, ignition timing and air/fuel ratio enleanment strategies to achieve rapid catalyst xe2x80x9clight offxe2x80x9d, thereby reducing emissions during cold-start conditions.
It is a third object of the invention to provide a system and method for reducing vehicle cold-start emissions which utilizes direct and/or indirect feedback to adapt ignition timing, air/fuel ratio enleanment, and valve timing events to achieve optimum emissions reduction and vehicle drivability.
It is a fourth object of the invention to provide a system and method for reducing vehicle cold-start emissions which utilizes variable valve timing events to expand the operational ranges of CSSRE ignition timing and air/fuel ratio enleanment schedules without deterioration of combustion quality and vehicle drivability (e.g., NVH issues).
It is a fifth object of the invention to provide a system and a method for reducing vehicle cold-start emissions which utilizes camless valve actuators to assist in fuel preparation during cold-start operating conditions.
It is a sixth object of the invention to provide a system and a method for reducing vehicle cold-start emissions which utilizes multiple valve events during a single intake stroke to reduce the amount of fuel deposited on a valve, thereby increasing evaporation of the fuel and improving combustion. Additionally, multiple openings of the intake valve may also improve combustion through better air/fuel mixture preparation by increasing in-cylinder fuel shearing and turbulence.
According to a first aspect of the present invention, a method is provided for reducing emissions of a vehicle of the type having an engine. The method includes the steps of detecting a cold-start condition; and selectively and synergistically altering valve timing, spark timing, and air/fuel delivery to the engine, effective to extend air/fuel enleanment limits, to improve combustion characteristics, and to increase exhaust gas temperature, thereby reducing cold-start emissions.
According to a second aspect of the present invention, a method is provided for reducing emissions of a vehicle of the type having an engine including a combustion chamber with at least one valve and a fuel injector which discharges an amount of fuel which is delivered to the chamber through the at least one valve. The method includes the step of selectively opening and closing the at least one valve multiple times during an intake stroke of the engine, thereby increasing vaporization of the amount of fuel, effective to increase combustion efficiency and exhaust gas temperature, thereby reducing emissions. Additionally, multiple openings of the intake valve may also improve combustion through better air/fuel mixture preparation by increasing in-cylinder fuel shearing and turbulence.
These and other features, aspects, and advantages of the invention will become apparent by reading the following specification and by reference to the following drawings.